Engel M (2008)
Publication Language: English
Publication Type: Thesis
Publication year: 2008
DOI: 10.18419/opus-4824
Complex crystals and quasicrystals are ordered states of matter with very large or even infinite unit cells. Their particle dynamics and defects differ significantly from what is known for simple crystals: Local rearrangements – phason flips – and new types of dislocations are consequences of the structural complexity. In order to understand their behavior at an elementary level, we introduce three model systems in one and two dimensions. The systems are studied analytically and with numerical simulations. (i) The structure factors of the dynamic Fibonacci chain are computed with high resolution. They show a characteristic broadening of the phonon dispersion relation. The particle motion in real space reveals soliton and breather modes, closely connected to phason flips. (ii) Using a tiling model for the intermetallic system AlPdMn, experimental observations of metadislocations and the collective particle dynamics are explained. The Burgers vectors of stable dislocations are derived from energy considerations. (iii) In the Lennard-Jones-Gauss system a surprising variety of two-dimensional complex crystals as well as a decagonal and two dodecagonal quasicrystals are grown. The particles reorder by phason flips at elevated temperatures. During annealing, the entropically stabilized quasicrystals undergo reversible phase transitions into complex crystals. Competing interparticle distances seem to favor structural complexity. With the Lennard-Jones-Gauss system the growth, equilibrium dynamics, and defects of quasicrystals and complex crystals can be studied in simulations for the first time.
APA:
Engel, M. (2008). Dynamics and Defects of Complex Crystals and Quasicrystals: Perspectives from Simple Model Systems (Dissertation).
MLA:
Engel, Michael. Dynamics and Defects of Complex Crystals and Quasicrystals: Perspectives from Simple Model Systems. Dissertation, 2008.
BibTeX: Download